linux-kernel - [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap

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Message-Id: <1448300202-5004-1-git-send-email-kwapulinski.piotr@gmail.com>
Date:	Mon, 23 Nov 2015 18:36:42 +0100
From:	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
To:	mhocko@...e.com
Cc:	akpm@...ux-foundation.org, oleg@...hat.com, cmetcalf@...hip.com,
	mszeredi@...e.cz, viro@...iv.linux.org.uk, dave@...olabs.net,
	kirill.shutemov@...ux.intel.com, n-horiguchi@...jp.nec.com,
	aarcange@...hat.com, iamjoonsoo.kim@....com, jack@...e.cz,
	xiexiuqi@...wei.com, vbabka@...e.cz, Vineet.Gupta1@...opsys.com,
	riel@...hat.com, gang.chen.5i5j@...il.com,
	linux-kernel@...r.kernel.org, linux-mm@...ck.org,
	Piotr Kwapulinski <kwapulinski.piotr@...il.com>
Subject: [PATCH v3] mm/mmap.c: remove incorrect MAP_FIXED flag comparison from mmap_region

The following flag comparison in mmap_region makes no sense:

if (!(vm_flags & MAP_FIXED))
    return -ENOMEM;

The condition is always false and thus the above "return -ENOMEM" is never
executed. The vm_flags must not be compared with MAP_FIXED flag.
The vm_flags may only be compared with VM_* flags.
MAP_FIXED has the same value as VM_MAYREAD.
Hitting the rlimit is a slow path and find_vma_intersection should realize
that there is no overlapping VMA for !MAP_FIXED case pretty quickly.

Remove the code that makes no sense.

Signed-off-by: Piotr Kwapulinski <kwapulinski.piotr@...il.com>
---
 mm/mmap.c | 3 ---
 1 file changed, 3 deletions(-)

diff --git a/mm/mmap.c b/mm/mmap.c
index 2ce04a6..42a8259 100644
--- a/mm/mmap.c
+++ b/mm/mmap.c
@@ -1551,9 +1551,6 @@ unsigned long mmap_region(struct file *file, unsigned long addr,
 		 * MAP_FIXED may remove pages of mappings that intersects with
 		 * requested mapping. Account for the pages it would unmap.
 		 */
-		if (!(vm_flags & MAP_FIXED))
-			return -ENOMEM;
-
 		nr_pages = count_vma_pages_range(mm, addr, addr + len);
 
 		if (!may_expand_vm(mm, (len >> PAGE_SHIFT) - nr_pages))
-- 
2.6.2

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